This invention relates to copper base alloys having excellent wear resistance, and more particularly, to dispersion hardened copper base alloys suitable for forming a wear resisting layer on a selected portion of a metallic substrate.
Several wear resisting copper base materials are known in the art, for example, from "Metallurgy Series 1--Constructing Materials and Their Heat Treatment--," Jul. 20, 1977, Japan Metallurgy Association, pages 20-25, including precipitation-hardened alloys such as Cu-Ni-Si alloys known as Corson alloy and Be-Cu alloys typically containing about 2% by weight of beryllium as well as dispersion hardened alloys having particles dispersed in a copper base matrix, the dispersion phase particles being composed mainly of hard oxides such as SiO.sub.2, Cr.sub.2 O.sub.3, BeO, TiO.sub.2, ZrO.sub.2, MgO, and MnO. The former copper alloys of the precipitation hardening type are hardened by carrying out a solution heat treatment and then aging for an extended period of time, thereby precipitating intermediate phases or inter-metallic compounds in the matrix. The latter copper alloys of the dispersion strengthening type are generally prepared by a sintering process comprising mixing copper or copper alloy powder forming a matrix with oxide powder forming a dispersion phase, and compressing the mixture followed by sintering. Also useful is an internal oxidation process comprising adding a metal more oxidizable than copper or copper alloy to copper or copper alloy forming a matrix, and holding the composition at elevated temperatures in an oxidizing atmosphere to thereby diffuse oxidizing gas into the matrix to form an oxide phase therein.
The precipitation-hardened alloys require an extended period of heat treatment at elevated temperatures because aging precipitation is accomplished by allowing diffusion to take place in a solid phase for a long period of time. The extended period of heat treatment at elevated temperatures is not adaptable to large-sized parts and often causes strain and other problems. Since particles precipitating in the alloys are as fine as several microns, the alloys are hard enough, but are insufficient in wear resisting performance, particularly in resistance to sliding wear. Better sliding wear resistance is obtained when hard particles having as large a diameter as about 10 to 100 microns are dispersed. It is difficult to precipitate such large diameter particles in the precipitation-hardened alloys.
The dispersion-strengthened alloys also have problems. As to the alloys strengthened by the internal oxidation process, the solid phase diffusion to produce dispersion phase particles requires a long period of treatment at elevated temperatures, which is not adapable to large-sized parts and causes strain and other problems as in the case of precipitation hardening. The dispersion-strengthened alloys by the sintering process have the advantage that dispersion phase particles may be grown to any desired diameter. However, it is difficult to form a layer of dispersion-strengthened alloy on a selected portion of a substrate because the entire material has to be compressed and sintered.
We proposed in Japanese Patent Application No. 61-303176 (U.S. Ser. No. 133,620 filed Dec. 16, 1987) a wear resisting, dispersion-strengthened copper base alloy having excellent wear resistance, especially sliding wear resistance which can be formed simply and easily on a selected portion of a metallic substrate by fusion welding or cladding, irrespective of whether the substrate is large or small in size. The dispersion-strengthened copper base alloy having excellent wear resistance is claimed in said application as essentially consisting of, in weight percent, 5 to 30% of nickel, 1 to 5% of silicon, 0.5 to 3% of boron and 4 to 30% of iron, the remainder being copper and unavoidable impurities, and having a structure in which hard particles composed chiefly of a silicide of an iron-nickel system are dispersed in a copper base matrix. Also claimed is a dispersion-strengthened copper base alloy of the above-mentioned composition further containing one or more of 0.1 to 5% of aluminum, 0.1 to 5% of titanium, and 1 to 10% of manganese. Also claimed is a dispersion-strengthened copper base alloy of the above-mentioned composition further containing 0.02 to 2% of carbon, and one or more of 0.05 to 10% of chromium and 0.3 to 5% of titanium wherein carbide particles are dispersed in the copper base matrix along with the iron-nickel system silicide.
The dispersion-strengthened copper base alloy of said application may be readily formed on a metallic substrate by fusion welding or cladding using a high density heat energy as given by a laser beam, TIG arc, plasma arc, and electron beam. The resulting alloy has a structure in which hard grains of a silicide of an iron-nickel system having a hardness of about 700 to about 1200 Hv and optionally carbide grains are substantially uniformly dispersed in a copper base matrix having a hardness of about 150 to about 250 Hv.
The dispersion-strengthened copper base alloy of said application is suitable to form an alloy layer on a selected portion of a metallic substrate and exhibits outstandingly superior wear resistance at approximately room temperature to conventional alloys. Through the follow-up experimentation, we have found that the wear resistance of this alloy is not yet fully satisfactory at elevated temperatures.